This invention relates to a manually-operable wire stripperxe2x80x94that is to say a hand tool for separating and at least partially removing an end portion of an outer layer of an elongate filamentary member having an inner core surrounded by said outer layer.
In the following, the invention will exclusively be defined and described with reference to the stripping of an electrical wire, having an inner core conductor and an outer insulating layer. It will however be understood that the invention may be used to remove an end portion of an outer layer surrounding a different kind of core memberxe2x80x94for example, an outer sheath surrounding a fibre optic cable. As such, the terms xe2x80x9cwirexe2x80x9d and xe2x80x9cinsulationxe2x80x9d as used herein should be interpret broadly.
There have been numerous designs of hand-held and manually-operated wire strippers, all of which aim at providing a tool which is easy to use, requires a relatively small operating force, and which can be manufactured relatively cheaply from few parts, without greatly compromising functionality. A further aim of many of these tools is to provide automatic adjustment so that no separate manual adjustment need be made to suit different wire diameters and insulation thicknesses.
One commercially successful wire stripper is described in EP-A-0,007,699. This tool has a pair of handles between which is mounted a complex cam mechanism arranged to close both a pair of wire clamping jaws and a pair of insulation stripping jaws, a link being arranged between one of the handles and the cam mechanism and which link together with the cam mechanism pass through a transition point between first and second stages of a stripping cycle. A disadvantage of this mechanism is that the velocity ratio between the handles and the stripping jaws is at its greatest when the stripping action is commenced, and at its smallest towards the end of the stripping cycle when the force required to displace the insulation is at its smallest. The consequence is that relatively high forces have to be applied to the handles in the initial stage of the stripping action, and that the length of insulation which may wholly be removed from the wire (as distinct from just displaced along the wire) is reduced. Those problems have already been considered for example in GB-B-2,077,517, which describes sophisticated cam mechanisms to optimise force transmission (ratios for both the cutting and stripping stages.
In my own earlier specification WO 94/21016 there is described a manually-operated wire stripper which addresses many of the short-comings of the known tools and in particular attempts to provide a mechanism which gives appropriate velocity ratios for the two stages of a stripping cycle. It is a principal aim of the present invention to improve on the wire stripper of this earlier specification in particular by allowing the manufacture of a compact stripping mechanism which lends itself to a right-angled construction (that is to say, a stripper where the handles project generally at right-angles to the line of action of the stripping jaws) and yet which still requires relatively low operating forces with a favourable stripping action.
According to the present invention, there is provided a manually-operable wire stripper comprising:
a body defining at its forward region a first wire-clamping jaw and at its rear a fixed handle;
a second wire-clamping jaw pivoted about a first axis to body and opposed to the fixed jaw for co-operation therewith to clamp a wire to be stripped, the first axis being displaced to one side of the centre-line of the pair of clamping jaws;
a pair of co-acting stripping jaws arranged between the damping jaws for sliding movement with respect thereto along the length of a damped wire, closing movement of the clamping jaws dosing the stripping jaws: and
an operating mechanism having;
an operating lever pivoted about said first axis to the body and extending across the line of sliding movement of the stripping jaws to project from the body, juxtaposed to the fixed handle for gripping therewith;
a draw-bar slidably mounted in the body and connected to the stripping jaws to effect said sliding movement thereof, the draw-bar defining a generally forwardly-facing first cam surface,
an arm projecting from the second clamping jaw and having a second cam surface, and
a roller located between the first and second cam surfaces and a rearwardly directed edge of the operating lever, the roller being driven by rearward pivoting movement of the lever;
the arrangement of the operating mechanism being such that during initial movement of the operating lever the roller is driven against the first and second cam surfaces to effect closing movement of the second wire-damping jaw until a wire to be stripped is clamped, whereafter continued movement of the operating lever drives the roller along the second cam surface thereby driving the draw-bar rearwardly through the first cam surface, to effect sliding stripping movement of the stripping jaws.
As will be appreciated from the embodiment of the invention described hereinafter, it is possible to configure the operating mechanism to occupy a relatively small volume without compromising performance of the wire stripper. Thus, the mechanism may still provide a relatively small stripping jaw movement at the commencement of the stripping action for significant operating lever movement, so maximising the power available at the first stage of stripping when the end portion of the insulation is partially cut and partially torn from the remainder of the insulation. In addition, the mechanism may provide a high degree of feedback to the damping force exerted by the clamping jaws, so that the clamping force is increased in the event that the stripping jaws have to exert a high force at the commencement of the stripping action, to detach the end portion of the insulation.
The mechanism may be configured to operate with a free roller by arranging said rear edge of the operating lever as a driving surface which engages the roller on rearward movement of the operating lever, provided the roller is otherwise constrained to remain between the first and second cam surfaces and the driving surface. Preferably, however, the roller is rotatably mounted to one end of a driving member, or between a pair of driving members, the other end of the (or each) driving member being connected to the operating lever.
It is known to allow both the stripping and clamping jaws to move apart at the conclusion of the stripping action. With the present stripper, this may be achieved by appropriate profiling of the second cam surface, so that as the roller approaches the limit of its movement in the stripping direction, the second clamping jaw is allowed to move away from the first camping jaw. In addition, or possibly instead, the body may define a fixed third cam surface arranged so that the roller runs along the third cam surface as the roller approaches the limit of its movement in the stripping direction. The third cam surface should be profiled so as to free the roller from the second cam surface and so to allow the second clamping jaw to move away from the first clamping jaw.
The pair of stripping jaws are preferably pivoted together about a second axis at their rearward ends and are connected to the draw-bar about that same axis. By providing a first spring between the stripping jaws, both those jaws and also the clamping jaws will be urged apart by the first spring. A second spring may be provided to urge the draw-bar forwardly, to an initial position where the mechanism is set ready to perform a stripping cycle.
The mechanism incorporated in a wire stripper of this invention lends itself to a series of appropriately profiled plates assembled together in a side-by-side manner. In such a case, the draw-bar should lie on the centre line of the clamping and stripping jaws and is constrained to perform essentially linear sliding movement substantially in alignment with the length of the first clamping jaw. Thus, the movement of the draw-bar causes the stripping jaws to slide along the length of the clamping jaws, to perform a stripping action. The draw-bar may be constrained by a guide plate secured to the body of the stripper, which guide plate may define the third cam surface, arranged to allow the second wire clamping jaw to unload the wire-clamping force. In addition, the guide plate may define a static cutter blade which co-operates with a moving cutter blade formed as a part of the operating lever. This gives the wire stripper the additional functionality of allowing the cutting of a wire to a required length.